1. Field of the Invention
The field of this invention relates generally to a method, system and apparatus for ferromagnetic wall monitoring, and more particularly to a method, system and apparatus for detecting flaws in pipe.
2. General Background of the Invention
Corrosion and wear commonly occurs in well pipe used in oil and gas production operations.
Various devices are known for detecting flaws in the walls of ferromagnetic pipe. For example, U.S. Pat. No. 4,510,447 (Moyer) discloses an apparatus that comprises an electromagnetic having poles in slideable contact with the surface of the wall of ferromagnetic pipe to form a closed magnetic circuit and means for electrically connecting the coil of the electromagnetic to an input source of alternating current whereby a fluctuating magnetic field is induced generally axially through the wall of the pipe between the poles of the electromagnetic.
U.S. Pat. No. 5,245,279 (Bendzsak) discloses a direct-current electromagnetic device for nondestructively detecting localized discontinuities in ferromagnetic objects. The device comprises an adjustable dc excitor means, a magnetic flux injector means, an external magnetic field detector means, a plurality of position sensors, a signal processing means and a control means.
U.S. Pat. No. 5,532,591 (Logue) discloses an apparatus for detecting surface flaws in cylindrical articles by means of asymmetric magnetic detection, utilizing a rotating magnetic field, said articles having central longitudinal axes, apparatus having a guide assembly for guiding the cylindrical articles along a displacement path having a central longitudinal axis extending coaxially of the central longitudinal axes of the articles and a pair of multiple polar sensor assemblies positioned in annular relationship with the displacement path for producing a plurality of phase/amplitude modulated signals representative of the surface geometry of the inspected cylindrical article, also disclosed are two embodiments of cylindrical container flange imperfection detector apparatus utilizing multiple polar sensor assemblies.
U.S. Pat. No. 5,537,035 (Fowler, et al.) discloses an apparatus and method for detecting anomalies in ferrous pipe structures. A sensor having one or more sensor shoe members is placed in the interior of a ferrous pipe structure to be inspected. Each sensor shoe member has one or more magnetic field generating apparatus, with a three-axis fluxgate magnetometer for detecting magnetic fields in the region of the ferrous pipe structure adjacent to which the sensor shoe member is placed. Any magnetic fields in the pipe structure, whether imposed externally, or remnant, which are detected, are sensed and resolved into components in three mutually orthogonal directions for enhanced accuracy.
U.S. Pat. No. 5,675,251 (MacLean, et al) and U.S. Pat. No. 6,087,830 (Brandly, et al.) disclose a device for inspecting the integrity of water distribution pipelines. The device is constructed of housing units, for housing inspection circuitry. The housing units are connected by flexible connectors which permit the units to move out of axial alignment to pass bends. The device is able to negotiate bends and pass through openings of reduced size in the pipeline. The device can be used with various inspection technologies including remote field eddy current inspection technology.
U.S. Pat. No. 6,104,024 (Hockey, et al.) discloses a magnet and sensor coil unilaterial and in relative motion to a conductive material, to measure perturbation or variation in the magnetic field in the presence of a flaw. A liftoff compensator measures a distance between the conductive material and the magnet.
U.S. Pat. No. 6,172,501 (Tsukada, et al.) discloses a detecting coil device mounted on part of a cable to evaluate the degree of corrosion of the cable, which is used, for example, on suspension or skew bridges. The detecting coil device is provided with a detecting coil and Hall elements. A magnetizer having a magnetizing coil is mounted as to enclose the cable and the detecting coil device. When current flows through the magnetizing coil, the current magnetizes the cable. The magnetic field strength is detected by the Hall element, and the amount of magnetic flux passing through the cable is detected using the detecting coil.
The foregoing references are incorporated herein setting forth part of the state of the art of the present invention.